200-301 review

200-301 review.Router WAN Interface StatusOne of the steps mentioned in the previous router LAN interface and LAN problems section about the IP routing troubleshooting process checks the interface status to ensure that the required interface is working. For a router interface to work properly, both interface status codes must be listed as up, which is often referred to by engineers as interface status "up/up".So far, the ICND1 and ICND2 books have only explored the basics of how the serial link works. Now, we know that the two links5.2 Basics 121routers must have their serial interfaces in the up/up state before they can send IPv4 packets to each other. The two routers should also have serial IP addresses on the same subnet.Later, the sections in Part 4 will explore further details of WAN links, including what routers need to forward IP packets using these links.Filtering Packets Using Access ListsAccess control lists (ACLs) can present a significant challenge in real-world troubleshooting. End-user packets sent by user applications are not the same as packets sent by testing tools such as ping and traceroute. ACLs sometimes filter ping and traceroute traffic, making network engineers think something is wrong when in fact there is nothing wrong. Or, problems with end-user traffic are caused by ACLs, but ping and traceroute traffic work fine because ACLs filter user traffic, not ping and traceroute traffic.This section summarizes tips for solving ACL-related problems in real life and on the exam. Step 1 Decide on which interface and which direction the ACL is enabled (show running-config,show ip interfaces) o Step 2 Decide which ACL statement matches the test packet (show access-lists,show ipaccess-lists) 0 Step 3 Analyze the ACL, predict which packet should match the ACL, focusing on the following points.a.Remember that the ACL uses the first matching logic.